Two hundred forty-two principals in secondary schools completed an opinion survey concerning the perceived causes of teacher ineffectiveness. The most frequently perceived causes were deficiencies in components of pedagogical knowledge--3 in-class components requiring student-teacher interaction (lesson-implementation skills, ability to establish rapport with students, and classroom-management skills), followed by 1 out-of-class component (lesson-planning skills). Deficiencies in content knowledge were the least frequently perceived cause. Principals in high- and low-performing schools produced similar ratings, except that lesson-planning skills were rated as more frequently a perceived cause of teacher ineffectiveness in low-performing schools. Alternative-certification programs that emphasize content knowledge and deemphasize pedagogical knowledge may fail to address the underlying causes of problems of teacher quality in schools.